The invention relates to a ground heating system which is suitable for the heating of runways, take-off and landing strips, bridges, parking areas and the like to avoid the formation of ice and to remove snow by causing it to melt. It could also be desirable to use such a heating system for installations to quickly dry such runways or tracks after a rain fall and to prevent aqua-planing.
It is known to heat earth or ground layers near the surface by conducting warm water or steam through a pipe circuit. It has also been proposed already to produce the required heat by means of electrical resistances. Generally it has been discovered that such installations have an inherent problem of providing a proper heat transfer. Due to the heat input the ground is dried out in the vicinity of the heating pipe and an efficient heat transfer thereafter is practically impossible.
From this consideration systems have been proposed wherein the ground layers to be heated are supplied continuously by a system of humidification. According to Dutch Patent No. 26777 this problem was solved in that two concentric tubes have been used wherein the inner tube is traversed by the heating medium and the outer perforated tube is supplied with water in order to maintain the degree of humidity of the ground at a constant level. The perforated tube may further be used as a draining medium. It is also known to locate the heating tube in a porous layer, for example of pebble stones, which permits a uniform water supply.
It has been found that these systems present a number of disadvantages. On the one hand the installation according to the Dutch Patent No. 26777 does not provide any means of maintaining a uniform degree of humidity in the ground and accordingly the heat flow in the direction of the ground surface is inadequate.
It is also known that uniform and rapid heating of the surface can only be obtained when the heat exchanging element presents a relatively large surface. Furthermore the heating element must be able to reach a high temperature so that an efficient and rapid heat exchange takes place. It is also favorable when the heating pipes are not located too far from the surface, but this increases the risk of damage of the pipes or of the electrical cables or resistances.